Radiation pyrometer



Nov. 17, 1942.

RELATIVE RESPONSE AND EMISSION M u A um m '0 5 E. F. KINGSBURY 2,302,554

RADIATION PYROMETER Filed April 29, 1939 2 Sheets-Sheet 1 RAT/0 0F RESPONSES 6 0 t (n o L400 I600 I800 2000 ABSOLUTE TEMPERATURE- A" //v VEN TOR By E ./-T K/NGSBURY M a/VM.

A TTORNE Y Nov. 17, 1942. mesa u 2,302,554

RADIATION PYROMETER Filed April I 29, 1959 2 Sheets-Sheet 2 MAMA/WWW I20 I40 Fla 6 P IN VENTOR By EFK/NGSBURY.

72 A TTORNEV Patented Now 17, 1942 RADIATION rmmmm Edwin F. Kingsbury, Rutherford, N. 1., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation or New York Application April 29, 1939, Serial No. 270,945

9 Claims. (Cl. 88-225) This invention relates to radiation pyrometers and more particularly to photoelectric radiation pyrometers based on color temperature.

proved photoelectric radiation pyrometer.

The principle underlying this invention is the simultaneous measurement of the relative radiations emitted by an incandescent source at two separated spectral regions utilizing radiation devices differentially connected and so controlled that their relative response becomes a measure of the temperature 02' the source. The temperature oian incandescent body can be measured by means of its emitted radiation in two ways. One of these is by utilizing the absolute intensity throughout either the entire spectrum or some restricted region. The other is by measuring the relative intensities emitted in two separated spectral regions. If the radiator is an ideal one, that is, if it is a black body, both methods are equally accurate and the choice becomes largely one of convenience. However, in practice radiators such as furnaces and incandescent surfaces depart more or less from the ideal condition and the method of measurement is dictated partially by considerations of accuracy. In such departures it is well known that methods based on absolute intensities suffer greater error than do those based on relative intensities. The embodiments of the invention described herein utilize the latter method and measure by simple means the color temperature rather than some radiation. or brightness temperature which the first method employs.

In an example of practice illustrative of this invention two radiant energy sensitive elements are employed, one element havinga maximum or effective response at one wave-length position and the other element having its maximum or eifective response at a different wave-length; position in the spectrum from that of the first element, these radiant energy sensitive elements Ming si multaneousiy irradiated from a common source of radiant energy Whose temxg'zemture is being measured. Radiation from hot body whose tenperature is to be measured collected into a beam and the rays focussed by a suitable lens system in an aperture and, upon passing theretlirough the rays are divided into two bu directed re spectively to two photoelectric a selenium photo-E. cell. as 'he other part to a thallium sulfide photo-T5. cell. The cells are electrically connected in opposing relation to an electric meter or in any other suitable diiierential arrangement.

cells, one part to obtain tcm. 55

perature indications, the electrical responses of the cells are preferably balanced against each other by adjusting the intensity oi the radiation impinging upon one of the cells, the selenium cell, for example, by means of a suitable absorption member or wedge positioned in the path 01 the rays directed to this cell. A null indication on an electric meter indicates a balance of the responses and by means of a calibrated scale attached to the absorption member, the temperature of the hot body is shown. Modified arrangements and applications oi the pyrom'eter are described hereinafter.

An advantage of a radiation pyrometer based on color-temperature is that such an instrument in-= dicates more clearly the true temperature of the radiator than other types of pyrometers. This is due fundamentally to the fact that the distribution of the intensity throughoutthe spectrum changes less in form than in absolute" mag nitude for incandescent radiators of practical interest. The measurement oi the relative response at two points therefore determines the form or shape of the emission curve and thereby the socalled color-temperature. In. this method, it is desirable to utilize two spectral wave-lengths or regions that are separated considerably since there is a greater variation of the ratio of response for a given temperature change and the practical accuracy of the method is thereby enhanced.

The color-temperature of a hot body is defined as the temperature of a black body which matches 1% color.

Other advantages or"; this pyrometer are high sensitivity, a high degree of accuracy, wide range oi temperature measurement, the absence of exterior factor such as the human eye for match-- ing colors or intensity of the radiations from the hot body whose temperature is measured. his pyrometer requires no battery and in any of its modifications is very simple.

A more detailed description of arrangements chosen for illustrating this invention follow.

his. 1 shows relative equienerev spectral v spcnse curves of two diilerent types (is. photoelec pyrometer in accordance with the principles this invention.

Fig. 3A shows details of the rotatable lightwedge arrangement of Fig. 3.

Figs. 4 and 4A show modifications of the pyrometer arrangement 01' Fig. 3 to use a "Polaroid" unit.

Fig. 5 is a schematic drawing showing the pyrometer arranged for continuous temperature indication.

Fig. 6 shows a circuit arrangement for applying the pyrometer to automatically control furnace temperature.

Fig. 1 is a typical set of curves showing the relative equienergy spectral response of two different photoelectric cells, the spectral emission of a black body at a temperature 1600 K. and at 2000 K. and the resulting response of each cell when excited by radiation from the black body at 2000 K. These curves are plotted with wavelengths along the abscissae and relative response and emission along the ordinates. Curve S shows the relative equienergy spectral response of a selenium cell over the range of the spectrum to which it is sensitive. Its range of response is between wave-lengths of about 0.3 to 0.7 micron and its maximum response occurs at about 0.57 micron which is in the yellow-green portion of the spectrum. Curve T similarly shows the relative spectral response of a thallium sulfide cell. Its range of response is between wave-lengths of about 0.7 to 1.15 microns and its maximum response occurs at about 6.98 micron which is in the infra-red portion or" the spectrum. Each of these curves shows the relative rather than the absolute response for various wave-lengths in the spectrum to which the cells are sensitive. In each case the maximum response is considered as unity and the relative response for other parts of each respective curve is shown with respect to this maximum. These two curves do not show the energy output of the two cells for if the curves were so plotted the ordinates for the two curves would be quite diiIerent. Curve J for a black body at a temperature of 2000 K. shows the emission over a band of wave-lengths to which both the selenium and the thallium sulfide cells respond. The emission of such a hot body is comparatively low in the region of wavelengths of about 0.5 micron and becomes very high in the region of about 1.1 microns. From this curve it is obvious that such a hot body will cause a comparatively small response in the shorter wave-lengths region in the selenium cell and a much greater response in the longer wavelengths region in the thallium sulfide cell provided they are more or less equal in absolute sensitivity. The resultant responses of the cells is shown by multiplying the relative responses of the cells by the emission from the black body. Such resultant curves for each cell irradiated by a black body at 2000 K. are shown, that marked SJ is for the selenium cell and that marked TJ is for the thallium sulfide cell. The heights and areas of these two curves, obviously from what has been stated above, do not indicate the absolute differences in response of the two cells, but are merely illustrative as the ordinates are not shown-in absolute units. It is the ratio of these two resulting, responses that is used in this pyrometer to indicate the temperature of a hot body. This ratio of emissions for a hot black body is difi'erent for difierent temperatures and consequently the resultant ratio 01' responses of the two cells is diflerent at diflerent te p atures of the hot body. To illustrate this a second curve J for a black body at a temperature of 1600 K. is shown for comparison with that at a temperature or 2000 K. From this it is obvious that the resultant responses or the two cells when irradiated by a hot body at different temperatures will vary according to the differing characteristics of the emission curves and consequently the ratio or the responses will vary for different temperatures.

Fig. 2 shows typical curve A of the ratio of the responses of selenium and thallium sulfide photo-E. M. F. cells at various absolute temperatures. This curve is a' plot of vs T where R5 is the response of the selenium cell. Rt is that of the thallium sulfide cell, and T the absolute temperature. The ratio of these responses, as shown by this curve, is different for different temperatures, and due to this fact various temperatures of a hot body may be ascertained by measuring the relative responses of two differently responding photoelectric cells and this fact is employed in the pyrometer of this invention as heretofore stated.

For photoelectric pyrometry it is not necessary to restrict the two eifective wave-lengths to visible wave-lengths giving an integral color match, but those appropriate to the responses of the cells which are employed in the apparatus, can be used as, for example, 0.62 and 1.0 micron for the selenium and the thallium sulfide cells, respectively.

Difierent types of radiant energy sensitive cells vary greatly in their effective color response. It is to be noted, however, that two similar light sensitive elements whose spectral responses are similarly distributed but whose effective responses are altered by means of suitable filters for causing the respective responses to occur at different frequency positions in the spectrum may be used. Either one or both such light sensitive elements may be equipped with a filter.

In this arrangement the two light sensitive cells have spectral response characteristics such that the ratio of their responses over a wide range of color-temperature varies continuously in the same direction, either increasingly or decreasingly as the temperature varies from one limit to the other. The greater the change per degree of temperature change the greater will be the sensitivity of the pyrometer.

Fig. 3 shows schematically a photoelectric radiation pyrometer based on color-temperature in which either two light sensitive elements inherently having their respective effective responses at different wave-lengths, or two similar light sensitive elements whose spectral responses are similarly distributed, but whose effective responses are altered by means of suitable filters for causing their respective responses to occur at different portions of the spectrum, are used. In using two similar light sensitive elements, either one or both may be equipped with a filter. The drawing and the following description for the sake of simplicity specifically consider the arrangement with the cells inherently having differently positioned maximum and effective responses. Also, while for illustration the two light sensitive elements are designated as the selenium and the thallium sulfide cells, other types may be used. These two types are well adapted to this combination as their respective maximum responses occur at quite different wavelength positions in the spectrum as disclosed in the description of Fig. 1 and also because they are photo-E. M. F. cells which obviate the use of a battery in the circuit of the system. The optical elements of the pyrometer are mounted in a suitable tubular housing it. A collecting lens to projects an image of a small area of the hot body i whose temperature is to be measured, which is shown within the heating chamber of an ordi nary electric furnace *2 at a suitable distance from the pyrorneter, on the plane of aperture iii bacl: of which ispositioned a suitable semitransparent dividing mirror which allows a part of the light to pass through it to the selenium cell 1 cells.

diaphragm 22 has an aperture somewhat larger than the beam passing through it this dia phragm prevents scattered light or radiations from. reaching the cells. In this arrarigerrieht both or the light sensitive cells are simultaneously irradiated. it essential both cells be ir radiated from the same area of the source which istalren care of by the requirement that the uniform and hottest area is imaged on fills the aperture common. to there. two light sensitive cells fill and are electrically connected in series-opposing relationship or db? ferentially to an electrical relay or measuring instrument iii conductors and An actjustable iris diaphragm positioned in the plane of the lens or as near thereto as practicable may be employed to limit magnitude of the radiation reaching the cells and thus largely eliminate any differences clue to the shapes oi the illuminationresponse characteristics of the two cells from the temperature measurements, and also to extehdthe useful temperature range of the pyrometer. in this manner it is possible to keep the current or voltage output of the cells within desired regions. l 'lheri the temperature of a hot body changes, it is well inseam that both the intensity and the color of the emitting radiator change. The output of a photoelectric cell is also affected by both of these factors. If the relation between intensity and photoresponse is a linear one for each cell, the absolute magnitudes of the responses due to this factor are immaterial since they are relatively always the same. However, when the intensity-response relation is nonlinear, it may then become desirable to work on restricted illumination region of the cells which can be accomplished in the manner described above for maintaining s milar illuminationresponse characteristics. With this arrangement the spectral or color-temperature of the hot body may be measured by balancing the exposures of the two cells by a variable absorption shutter or Wedge member Gil, positioned in front of one of the cells and controlling a calibrated scale. The absorption wedge Bil mounted on support 6! which does not obstruct the optical portion of the wedge, may be either reciprocable or rotatable andis here shown as rotatable on shaft 62. A plan view of the wedge unit is shown in Fig. 3A. The scale 63 calibrated to indicate temperatures may be attached to the wedge near its edge or circumference so as to move with it and a fixed pointer 64 indicates the temperature readings. A balance of the exposures of the two cells is indicated by a null indication of electrical meter 10. When the response of the two cells is balanced by adjusting the absorption wedge.

68, the temperature of the hot body is directly shown by the calibrated scale controlled by the position of the absorption wedge 66.

While light sensitive cell 50 has been designated as a selenium cell and 50 as a thallium sulfide cell, it is not essential which positions these cells occupy. This is determined by the characteristics of the transparent dividing mirror till which. can be a semitransparent metallic mirror on glass. Such a mirror, especially of gold, reilects the infra-red rays better than the visible so that the thallium sulfide cell is naturally placed in the path of the reflected radiations. An appropriate fixed absorbing screen iii in front of the thallium sulfide cell may be used to obtain the desired initial relative exposures of the two The position of this absorbing screen at is not changed in making temperature measure" merits. Also, the variable absorption wedge may be positioned in front of either light sensh tire cell.

Figs. i and all show modified arrangements for balancing the exposures oi the two photocells in which, in place of the usual light absorption wedge, a Polaroit. unit is employed for varying the relative amounts of radiation reaching the two cells. Polaroid is made of a material like quinine iociosulphate and has the property of polarizing light. A. polarizing unit is made up of two relatively adjustable parts, a polarizer and an analyzer. By means of unit, controlled amounts of light may be transmitted. lt is effective particularly in the range of the spectrum between the infra-red and the blue portions but is largely transparent and ineffective as a polarirser in the infra-red. It is. therefore, prelerably employed in the path of the radiations reaching the selenium cell. In the modified arrangement a rotatable Polaroid disc are is substituted for the absorption wedge lit) and a stationary Polaroid element see is positioned in optical alignment in front of the selenium cell so thatbotl'i are in the path of the radiations reaching this cell, as shown in Fig. 4. The elements of this polarizing unit may be differently positiohed,'for example, the rotatable Polaroid disc 5GP may be positioned nearer the lens while the stationary Polaroid" element may be positioned in the same common beam, as shown in Fig 4A, or immediately front of the selenium cell. The positioning of the Polaroid element in the common beam is pos sible because Polaroid" is practically transparout and without effect in the infra-red where the thallium sulfide cell is responsive, while on the the selenium cell responds. If the two cells have equal response, say at l200 K, then at a higher temperature theselenium will give more response necessitating a reduction in its irradiation. Any residual disturbance of the illumination on the thallium cell or effective polarization by the mirror can be allowed for in the calibrating of the scale in the arrangement employing the Polaroid unit.

In the arrangement as described above, the relative amounts of radiation reaching the cells may be varied by a suitable variable absorption element or polarizing unit to cause the responses of the two cells to equal or balance each other and by calibration of an indicating scale associated with the variable element, the temperature is directly shown for every balance setting.

4 However, for a given setting 01' the variable absorption unit this arrangement may be made self-indicating within a comparatively narrow range by calibrating the scale of the electrical meter so that its indications show the temperatures directly. Such an arrangement, however, is not as desirable as that in which the responses of the two cells are balanced for each temperature reading.

Continuous temperature indications may be automatically obtained by methods well known to the art by using the electrical instrument 10 as a relay to control mechanism which in turn 'automatically adjusts the absorption unit so that the responses of the cells are quickly balanced at all times and the scale associated with the absorption unit then continuously indicates the temperature.

Fig. 5 shows the pyrometer arranged for continuous temperature indications. The electrical relay ii is equipped with contacts connected in a local circuit leading to an automatic adjusting mechanism 30 consisting of a motor control relay reversing switch mechanism 8| governing the operation oi motor 82 which is geared to the rotatable member 59 of the absorption unit. The automatic adjusting mechanism 80 may be of any well-known type such as shown in Patent 1,703,142 issued to E. E. Green, February 26, 1929. When the responses or the photoelectric cells of the pyrometer are balanced the contacts 01 relay ii are open and the motor 82 is at rest. A change of temperature oi. the irradiating body causes an unbalance and one or the other of the contacts of relay ii closes which, in turn, causes the operation of motor 82 in a direction to rotate the movable member 60 of the absorption unit to rebalance the photoelectric cells when the relay ii again takes its neutral or open circuit position and the motor 82 stops. Power for operating the motor and the reversing switch mechanism of the adjusting mechanism 80 may be supplied through circuit connection 20!. The absorption unit is thus automatically adjusted in either direction depending upon whether the temperature of the irradiating body is rising or falling and continuous temperature indication is obtained anclindicated by the scale 83.

The non-adjusting or non-seli-indicating pyrometer arrangement may be used for automatic control at a given temperature setting by substituting for the electrical meter a relay equipped for controllng the temperature control mechanism associated with a furnace or other heating device.

Fig. 6 sh we a circuit arrangement for applying the pyrometer to automatically control furnace temperatures. The winding Iiii of gal vanometerlet, schematically shown in the drawing, is connected to conductors l2 and 13 of the output circuit of the pyrometer and by means of a light beam L deflected either to the left or the right oi" its neutral position by the operation of the galvanometer one or the other of two photo-electrically energized relay circuits is caused to operate, which in turn controls other relay apparatus arranged to cause a decrease or an increase in the furnace current. When the light beam L from the galvanometer relay Hill moves to the left it impinges on photoelectric cell H0 and energizes relay ill which closes its contacts H2 and causes energization of relay i2! whose contacts 122 in turn open and remove the short circuit from resistance I20 which is in series with the heating element of the electric furnace 2. This reduces the current going through the furnace and consequently its temperature. When the light beam L 01' the galvanometer relay I" moves to the right it impinges on photoelectric cell I" and energizes relay l3| which closes its contacts III and causes energization of relay Ill whose contacts ill in turn close and short-circuit the resistance ill in series with the heating element of the furnace 2 thus increasing the current flow therethrough and causing a rise in the furnace temperature. The two circuits associated with the light sensitive cells H0 and I" are practically identical except that the contacts on relay iii are normally closed when non-operated, while on the corresponding relay ill the contacts are open when in non-operated position. These two relays can be replaced by or can in turn control mercury tilting switches connected in the same manner to the control resistances. Any suitable source or power may be used for operating the main relay switches by connection with circuits 202 and 20! and for supplying power to the electric furnace or other current consuming device by connection with circuit 204. In the operation or this arrangement the light beam from the galvanometer relay I00, which is connected in the photoelectric cell circuit of the pyrometer, is positioned in a neutral position when the furnace is at the desired temperature so that it does not impinge upon either of the light sensitive cells ill] and I30. The pyrometer then obviously will automatically cause an increase or a decrease in the current supplied to the furnace as required to maintain it at substantially constant temperature.

What is claimed is:

l. A photoelectric radiation pyrometer comprising two radiant energy sensitive elements, an opaque member having an aperture, a lens system for collecting radiations from a body whose temperature is to be measured and iocussing a beam 01' said radiations at said aperture, said aperture being of a size to transmit only radiations focused thereon by the lens, optical defleeting means positioned in and dividing said beam after passing through said aperture into two channels in which said sensitive elements are respectively positioned, an optical member having varying absorption positioned in one oi said channels, means for adjusting said absorbing member for controlling the amount of radiation reaching one of said sensitive elements, and an electric instrument connected in the output circuit of said sensitive elements for indicating the relative response of said sensitive elements.

2. A photoelectric radiation pyrometer comprising a selenium photo-E. M. F. cell and a thallium sulfide photo-E. M. F. cell, an opaque member iaving an aperture, a lens for collecting radiations from a body whose temperature is to be measured and focussing a beam of said radiations at said aperture, said aperture being of a size to transmit only radiations focused thereon by said lens, optical deflecting means positioned in and dividing said beam after passing through said aperture into two channels in which said cells are respectively positioned, an optical member having varying absorption positioned in one oi said channels, means for adjusting said absorbing a wave-length of approximately 1.0 micron, a third transverse partition between said lens and said first partition having a central aperture slightly larger than the cross-section at the plane of said central aperture of the light beam passing from said lens through the aperture in said first partition, a fixed absorbing screen in front of said thallium sulfide cell to provide a desired initial relative exposure 01' said two cells, a polarizing shutter unit in front of said selenium cell comprising a stationary sheet of polarizing material comprising quinine iodosulphate and a rotatable sheet of the same material. partially within and partially without said tubular housing, means to rotate said rotatable sheet, a zero-center ammeter, electrical connections between said ammeter and said cells connecting said cells in series-opposing relationship to said ammeter, and a fixed scale on said rotatable sheet indicating temperature of the body under test when said sheet is positioned to give v a null reading on said meter.

9. A photoelectric radiation pyrometer comprising a selenium photo-EMF. cell and a thallium sulfide photo-EMF. cell, an opaque member having an aperture, a lens for collecting radiations from a body whose temperature is to be measured and focusing a beam of said radiations at said aperture, said aperture being oi a size to transmit only radiations tocused thereon by said lens, optical deflecting means positioned in and dividing said beam after passing through said aperture into two channels in which said cells are respectivey positioned. an optical member having varying absorption positioned in one of said channels, means for adjusting said absorbing memberior controlling the amount of radiation reaching one of said cells, and an electric instrument connected in the output circuit oi said cells for indicating the relative response 0! said cells, wherein the means for adjusting said absorbing member for controlling the relative amount 0! radiations reaching said cells is automatically operated, and said electric instrument is electric relay means connected in the output circuit of said cells for causing said automatic adjusting means to maintain a balance 01' the relative response or said cells.

EDWIN F. KINGSBU'RY. 

